A balance audit compares where your hours go with where your gaps are. In Cambridge IGCSE Combined Science 0653 you revise biology, chemistry and physics together, so the audit stops one science from quietly taking the whole week. It belongs at the start of every revision week in 0653 revision and route planning.
How does the audit work?
The idea is simple: your hours should follow your gaps. Build it in four steps.
- List the syllabus statements for your route and year, science by science. Use the Cambridge syllabus your school confirms.
- Tick each statement you cannot yet answer on a fresh question, without notes. Those are your gaps.
- Count the gaps in each science and add them up.
- Share your hours in proportion: hours × (science gaps ÷ total gaps).
Round to one decimal place and check that the shares add back to your total hours.
Worked example
This is an invented log, not real exam data. A student has 12 hours this week. Her unrevised statements: biology 20, chemistry 18, physics 24.
Step 1, total gaps: 20 + 18 + 24 = 62.
Step 2, shares of need: biology 20/62 = 32.3%, chemistry 18/62 = 29.0%, physics 24/62 = 38.7%.
Step 3, hours: biology 12 × 20/62 = 3.87, so 3.9 h. Chemistry 12 × 18/62 = 3.48, so 3.5 h. Physics 12 × 24/62 = 4.65, so 4.6 h (rounded so the total stays at 12.0 h).
Step 4, check: 3.9 + 3.5 + 4.6 = 12.0 h.
Her old plan was 6 h biology, 3 h chemistry, 3 h physics, which is 50%, 25% and 25%. Physics had the biggest need and the smallest share.
What is the mistake to watch for?
Planning from preference. The student above gave biology half the week because it felt friendly and she could finish tasks quickly there.
Mistaken plan: 6 h / 3 h / 3 h, justified as “I am better at biology, so it will be quick to cover”.
A strong feeling is not a count. Her tick list shows 20 biology gaps, and 24 in physics.
The correction is to let the count decide, then adjust only for a stated reason, such as a test next week in one science. Write that reason beside the plan.
Check yourself
1. With 8 hours, unrevised statements are biology 10, chemistry 5, physics 5. How many hours does each science get?
Show answer
Total gaps 20. Biology 8 × 10/20 = 4 h. Chemistry 8 × 5/20 = 2 h. Physics 8 × 5/20 = 2 h. Total 8 h.
2. A plan gives 4 h to each of the three sciences (12 h). Gaps are biology 6, chemistry 12, physics 6. What is the audited split?
Show answer
Total gaps 24. Biology 12 × 6/24 = 3 h. Chemistry 12 × 12/24 = 6 h. Physics 12 × 6/24 = 3 h. Chemistry is under-planned by 2 h.
3. A student spends 9 h of a 12 h week on one science. What percentage is that, and what should she check?
Show answer
9/12 = 75%. She should check whether that science really holds about three quarters of her gaps. If it does not, hours are being spent on comfort.
Where this leads next
Next, see how to reuse a shared concept without duplicating its article, which saves hours inside each science. Then test yourself with the mixed practice set.
If you want a second pair of eyes on your tick list, our teachers can help in online one-to-one Combined Science tuition.